A 4.8 V Reversible Li2CoPO4F/Graphite Battery Enabled by Concentrated Electrolytes and Optimized Cell Design

Abstract Elevating the voltage of lithium‐ion batteries (currently 3.8 V) is a simple and pragmatic way to achieve high‐density energy storage. Many so‐called “5 V‐class” cathodes have been discovered over the past decade; however, they have been studied below 5 V ( vs . Li/Li + ) because of the severe oxidation of electrolytes and other cell components. Here, highly reversible charge‐discharge cycling of Li 2 CoPO 4 F/graphite full‐cells up to a cut‐off voltage of 5.2 V is demonstrated for the first time. This result is achieved with synergetic effects of an optimized cell design and a newly designed concentrated electrolyte based on LiBF 4 , propylene carbonate (PC), and fluoroethylene carbonate (FEC). As an electrolyte design rationale, two important properties of high oxidation stability and anode‐passivation ability are clearly allocated for LiBF 4 and FEC, respectively. Besides, all other cell components (e. g., conductive carbon, separator, and binder) are reconsidered and customized for use at >5 V. The new concentrated electrolyte and optimized cell design presented here will pave the way for developing over‐5 V rechargeable batteries.